Cigarette filter

ABSTRACT

Tobacco smoke filter having an axially extending tubular outer member and an axially extending air permeable inner member therewithin. The inner member is formed of filaments or fibers bonded to each other at their points of contact. At a first position the outer surface of the inner member is in engagement with the inner surface of the outer member to at least substantially preclude axial passage of smoke therebetween while at a second position, longitudinally spaced from the first, the filaments or fibers are formed into a portion of substantially smaller cross section to leave a hollow space through which smoke drawn through the filter may pass.

[ 51 Sept. 12, 1972 United States Patent Davenport I CIGARETTE FILTER 3,224,453 12/1965 Mahoneyetal...........13l/268 Francis-Robert Davenport, Ashtead, 3,533,416 10/1970 Berger et a1...............13l/266 England [73] Assignee: American Filtrona Corporation,

[72] Inventor:

Primary Examiner-Melvin D. Rein Attorney-Holman & Stern Richmond, Va.

Oct. 1, 1970 22 Filed: ABSIRACT Tobacco smoke filter having an axially extending tubular outer member and an axially extending air permeable inner member therewithin. The inner member is formed of filaments or fibers bonded to each other at their points of contact. At a first position the outer surface of the inner member is in engagement with the inner surface of the outer member to at least substantially preclude axial passage of smoke therebetween while at a second position, longitudinally spaced from the first, the filaments or fibers are formed into a portion of substantially smaller cross section to leave a hollow space through which smoke drawn through the filter may pass.

m mmm mm M73 mod n B m m H mm mum 0 cc an 2 4 h "n" 1 p n. m h A m m n m.% m m e 1 n" a L l in 0 D. F v .M 0.. on .m. A NJ U1 1]] l 0 2 8 2 3 555 References Cited UNITED STATES PATENTS 16 Claims, 8 Drawing Figures 3,040,752 6/1962 Ganz l 3 1110.9

PATENTEU 12 9 3.690.326

sum 2 or 2 I nvenlor Fmnus Roezm- VMnumk-r CIGARETTE FILTER The present invention relates to a tobacco smoke filter especially for use in cigarettes. Cigarette filters are already known comprising crimped fibers or filaments which are bonded to each other at points of contact to form air permeable deformation resistant rods. A suitable filamentary material from which to make filters is crimped continuous filamentary cellulose acetate tow, commonly referred to as cigarette tow. This comprises an assemblage of several thousand crimped filaments whichare converted into tobacco smoke filter rods by deregistering the crimps, separating the filaments from each other, applying a bonding agent, commonly a solvent plastiscizer, bringing the filaments together to form a rod, activating the bonding agent by the application of heat or allowing it to act, at a slower rate, at ambient temperatures and finally cutting the rod into lengths. A filter made by this process comprises a structurally unitary rod of crimped cellulose acetate filaments each filament extending without break from one end of the rod to the other.

'Tobacco smoke filters are also known comprising fibers of finite length part of which may be arranged transversely of the rod or lie without a distinct orientation with respect to it. Such filters may be made from the'crimped continuous filamentary tow by applying a bonding .agent, cutting the filaments into fibers, rearranging them in the desired orientation, forming them into a rod activating the bonding agent and finally cutting the rod into lengths.

It will be clear from the above that the filters made from continuous filamentary material without the intermediate cutting step comprise fibers the length of which is at least as great as the length of the filter. Since the length of the filter is limited the length of any filament that runs from end to end is similarly limited so that such filters comprise fibers of finite length which are approximately as long as the filter. Thus the term fibers in the claims of this specification includes both fibers which have a finite length before they are formed into a filter rod and those which are given their finite length by the cutting operation of the filter making apparatus.

The percentage of tobacco smoke particles which are retained by the filters referred to above is dependent on the pressure drop of the rod and the denier of the fibers or filaments of which it is comprised. The filters comprising fibers of finite length may have a somewhat greater retention of tobacco smoke particles at a given pressure drop then the filters of continuous filaments.

The primary object of the present invention is to provide a tobacco smoke filter comprising fibers which are bonded to each other at their points of contact and which have at a specified pressure drop an improved retention of tobacco smoke particles.

The method for making the filters is described in detail using as a starting material continuous filamentary cellulose acetate and the filters produced comprise such continuous filaments. The method is, however, applicable to the filters made from fibers of finite length. Its application thereto will be readily apparent to those skilled in the art.

The invention provides a tobacco smoke filter having an axially extending tubular outer member, within said member an axially extending air permeable inner member comprising an air permeable rod of filaments or fibers which are bonded to each other at their points of contact, at a first position the outer surface of the inner member being in engagement with the inner surface of the outer member so as substantially to preclude axial passage of the smoke between the members whilst at a second position, longitudinally spaced from the first, the filaments or fibers are formed into a portion of substantially smaller cross sectional area to leave a hollow space through which smoke drawn through the filter may pass. The area of the rod bounding the space at the second position is substantially greater, preferably four times as great as the cross sectional area of the rod at the first position.

In manufacturing the filters of the invention, the steps include forming an air permeable inner member comprising an axially extending rod of binded filaments or fibers, deforming it at longitudinally separated positions to agglomerate the filaments or fibers in portions of substantially smaller cross-sectional area, enclosing the said member by an axially extending tubular outer member and bringing the inner surface thereof into engagement with the outer surface of the inner member. The deformation of the rod must be sufficient to cause its cross sectional area substantially and permanently to drop, so that its pressure drop as herein defined, is substantially less than before deformation. Preferably such a drop should not be less than 30 percent.

FIG. 1 shows a perspective view, with parts removed, of a cigarette filter element attached to a paper wrapped tobacco rod.

FIG. 2 shows an elevation of the inner member of the filter of FIG. 1.

FIG. 3 shows a transverse cross section along lines IIIIII of FIG. 2.

FIG. 4 shows a view of an alternative form of the inner air permeable member.

FIG. 5 shows a transverse cross section along lines VV' of FIG. 4.

FIGS. 6 and 7 show further forms which the inner member of the filter element may have.

FIG. 8 shows in diagrammatic form an apparatus for carrying out the method of manufacture.

Referring now to FIGS. 1, 2 and 3 an embodiment of the invention comprises a rod 1 which forms the inner member, made of crimped continuous filaments of cellulose acetate which are bonded to each other at their points of contact. End portions 2 and 2' of the rod 1 have a circular cross section and a center portion 3 has a cruciform cross section. The tips 4 of the ribs 5 of portion 3 lie upon a circle coaxial with and having the same diameter as that of the portions 2 and 2'. The filaments within the ribs 5 from the tips 4 to the axis 6 are closely agglomerated so that the fiber density is far greater than in the portions 2 and 2'. The part of the rod 1, lying between the parts of the rib 7 and 7' and the. dotted lines 8 and 8' is tapered, air permeable, and fibrous, the density gradually decreasing from 7 and 8 and from 7 and 8'. Surrounding the rod 1 is a substantially impermeable tubular paper wrapper 9 which is tightly engaged about the circumferential surface of the rod at the parts 2 and 2'. Thus no significant bypass of smoke occurs between the surface of the rod and the inner surface of the enveloping paper wrapper 9. Advantageously the rod 1 and the wrapper 9 may be sealed, e. g., by means of an adhesive.

The filter is attached to a paper wrapped tobacco rod 112 by an enveloping overlapping strip 15, of cork tipping paper. Upon drawing smoke from the lighted end 13, in the direction shown by the arrow it will pass through the portion 2' at the upstream end of the filter element and, meeting great resistance in the ribs 5, pass through the surface of the tapering portion of the rod lying between 7 and 8 into the spaces 14 surrounding the ribs, thence into the portion 2 at the mouth end of the cigarette.

The filter element shown in FIGS. 1, 2 and 3 was made as follows. Cylindrical rods 25 mm long having the circular cross section of the portions 2 and 2 were manufactured in accordance with British Pat. No. 1,169,932 from crimped continuous filaments of cellulose acetate. These were placed in a device having four heated mating dies. Each die comprises a central part, having a V-shaped cross section, at each side a sloping part. These dies gripped and deformed the-rod around the center of its-length into the crimped portion 3 and tapering portions at each end of the crimped portion. The heat caused the cellulose acetate filaments at the crimped portion 3 to fuse superficially and adhere with very little space between them. Afterdeformation, the rod was tightly wrapped by a strip of paper to form the tube 9, the paper being held in place by a lapped and stuck seam.

The pressure drop of a cigarette filter is defined as the pressure needed to draw 17.5 cc per second of air through it. When a fibrous or filamentary rod is deformed according to the method of the invention its pressure drop falls but the ratio of the tar retention to the pressure drop rises. The greater is the fall in the pressure drop the greater is the improvement in the above ratio. In general the best tar retention/pressure drop ratio is found when the denier of the filaments is below 5.0, preferably 2.5. The weight per unit length of the filters is substantially constant the filaments being I pressed into a small cross-sectional area, as seen in FIGS. 3 and without stretching or compressing them much in the longitudinal direction. The shape of the deforming dies should be such that the area of the rod through which the smoke passes to enter or leave the space should be, for best results, at least four times as great as the cross-sectional area in the undeformed portion of the rod.-

In FIGS. 4 and 5 an example of an air permeable inner member 20 is shown. It has two ends 21 and 21' which have a circular cross section between which lies a portion 22 around which parts 23 and 23' taper almost to a point and are surrounded by three ribs 24 of which the tips 25 lie upon a circle coaxial with and having the same diameter as the portions 21 and 21. To form the tobacco smoke filter element of the invention this is tightly enveloped so as to seal around portions 21 and 21 by a wrapper such as the wrapper 9 shown in FIG. 1 and thereafter attached to a cigarette rod by means of a tipping material such as the cork tipping paper of FIG. 1. Alternatively the tipping paper 15 may be wrapped around inner member to seal the portions'Zl and 21 to its inner surface and at the same time to attach the tobacco rod 12. Thus the tipping paper serves as means of attachment to the tobacco rod and as the tubular outer member.

The inner member 50 of FIG. 6 resembles the inner member 1 of FIG. 1 in all respects except that the center is cylindrical and the crimped ends 51 and 52 are cruciform. The inner member 55 of FIG. 7 comprises one cylindrical portion 56 one crimped cruciform portion 57 and between them a tapering portion 58, and alternating ribs and valleys 61. The inner members 50 and 55 are employed in the same way as the inner member 1 of FIG. 1 and have similar filtering effects.

The portion of the rod having a substantially reduced cross-sectional area need not comprise ribs having a Y- shaped or cruciform arrangement but may have any convenient form. It should give the smoke a greater area through which to pass into the undeformed portion or portions. It should cause the pressure drop to fall below that of a rod of identical composition and of constant cross-sectional shape.

Referring now to FIG. 8, an embodiment of the method of manufacturing tobacco smoke filter elements, in this case from cellulose acetate filaments is shown. A known apparatus 30 for example that described in British Pat. No. 765,961 is supplied with crimped cellulose acetate filaments. It separates the filaments and deregisters their crimps, applies to the filaments a fine spray of glyceryl triacetate and delivers a band 31 of the filaments to a rod forming device 32 in which they are formed into an unwrapped deformation resistant continuous cylindrical rod 33, for example by use of the method described in British Pat. No. 1,169,932. In the deforming device 34 the continuous rod is shaped at the desired locations into a continuous rod 36 comprising continuous alternating portions such as those shown in FIGS. 1-7, by heated crimping members which enter and leave the path of the rod 33 and compress spaced portions into a form having a substantially reduced cross-sectional area. The crimping members may comprise reciprocating or rotative members. These have mated deforming surfaces arranged and driven in synchronism with the movement of the rod 33 to produce the shaped portions of reduced cross-sectional area in the deformed rod 36 which emerges. A bobbin 40 supplies a continuous strip 41 of paper which passes to garniture 42 where it is enwrapped around continuous rod 36 to form the tubular outer member. The edges of the strip 41 are overlapped and held in place by a lapped and stuck scam in a known manner. A tape drum 44 drives a tape 43 through the garniture 42 and past tensioning roller 45. A heater 46 dries the adhesive in the seam in the tubular outer member so as to complete the formation of a continuous rod 47 which contains a unitary succession of portions of bonded filaments the cross-sectional area of which changes from place to place along its length. A cut-off 48 divides the rod 47 approximately equidistantly between the positions of deformation into multiple length filter rods 50 each of which contains a number of deformed and undeformed portions. The cut is made only through deformed portions to produce filters having inner members such as those of FIGS. 6 and 7. It is made through the undeformed portions to produce filters having inner members such as those of FIGS. l-5. The rods 50 are used in the usual way that is they are divided by the filter cigarette machines into double length pieces, each of which is assembled to a tobacco rod at its ends and cut in its center to produce filter cigarettes.

Any space between the inner member and the tubular outer member may be filled with particles or granules of filtering material such as active carbon, thermoplastic foam or fine denier bonded filaments. To facilitate the filling of the space by the filtering material the crimp preferably has the form of a single straight rib. When making such a filter by the method of FIG. 8 the paper strip 41 is formed into a U around the rod 36 and the granules dropped on to each deformed portion to flow on each side of the rib. The gamiture' 42 folds and adheres the strip 41 to hold the granules in place.

EXAMPLES Filters were made in accordance with the method described above from crimped continuous filaments of cellulose acetate. The results are summarized in the table. Under Tow the filament and total deniers are given and the percentage tar retention of the prior art filters (of uniform cross section, and made of the same tow and lengthened to give the same pressure drop as the filters of the invention) are quoted for purposes of comparison.

Y center see FIGS. 4 and 5. center see FIGS. 1, 2 and 3. at one end see FIG. 7. at each end see FIG. 6.

What is claimed is:

l. A tobacco smoke filter comprising:

a. an axially extending tubular outer member having an inner surface,

b. within said outer member an axially extending air permeable inner member comprising an air permeable rod of fibers which are bonded to each other at their points of contact, said inner member having an outer surface,

c. at a first longitudinal position, the outer surface of the inner member being in engagement with the inner surface of the outer member over a complete circumferential ring so as substantially to preclude axial passage of the smoke between said inner and outer members at said first position,

d. at a second longitudinal position, longitudinally spaced from said first position, the fibers of which the rod is comprised being formed into a portion of said rod at said first position, the density of said rod at said second position being greater than the density of said rod at said first position,

e. said rod having an intermediate outer surface between said first and second positions, at least a portion of said intermediate outer surface bein spaced from and lying within, said inner surface 0% said outer member, cavity means defined in part by said intennediate outer surface portion and a portion of said inner surface of said outer member and being closed at least at one end by portions of said circumferential ring, and

f. the area of said intermediate outer surface portion being greater than the transverse cross-sectional area of said rod at said first position.

2. A filter according to claim 1 characterized in that said area of said intermediate outer surface portion of said inner member is at least four times as great as said cross-sectional area of said rod at said first position.

3. A filter according to claim 1 characterized in that said portion of substantially smaller cross sectional area is longitudinally spaced from the ends of the filter.

4. A filter according to claim 1 characterized in that said portion of substantially smaller cross-sectional area lies at one end of the filter.

5. A filter according to claim 4 characterized in that both ends of said inner member have a cross-sectional area substantially smaller than the intermediate portlon.

6. A filter according to claim 1 characterized in that at said second position the fibers are formed into ribs.

7. A filter according to claim 6 characterized in that the ribs are arranged in the form of a cross.

8. A filter according to claim 6 characterized in that the ribs are arranged in the form of a Y.

9. A filter according to claim 6 characterized in that the tips of the ribs lie upon a circle, the diameter of which is approximately equal to the internal diameter of the said outer member.

10. A filter according to claim 1 characterized in that between said first and second positions said intermediate outer surface portion of said inner member through which the smoke passes is formed with protrusions or depressions.

11. A filter according to claim 10 characterized in that the said protrusions or depressions comprise longitudinally directed ribs or valleys.

12. A filter according to claim 1 characterized in that the fibers have a denier of less than 5.

13. A filter according to claim 12 characterized in that the denier of the fibers is not greater than 2.5.

14. A filter cigarette comprising a tobacco rod and a filter according to claim 1, said outer member of the filter comprising a tipping material which is wrapped around said inner member and extends over a part of the tobacco rod to attach the filter thereto.

15. A filter according to claim 13 characterized in that the fibers are of cellulose acetate.

16. A filter according to claim 1 in which the weight substantially smaller transverse cross-sectional Per unitlengthis Substantially constantarea than the transverse cross-sectional area of 

1. A tobacco smoke filter comprising: a. an axially extending tubular outer member having an inner surface, b. within said outer member an axially extending air permeable inner member comprising an air permeable rod of fibers which are bonded to each other at their points of contact, said inner member having an outer surface, c. at a first longitudinal position, the outer surface of the inner member being in engagement with the inner surface of the outer member over a complete circumferential ring so as substantially to preclude axial passage of the smoke between said inner and outer members at said first position, d. at a second longitudinal position, longitudinally spaced from said first position, the fibers of which the rod is comprised being formed into a portion of substantially smaller transverse cross-sectional area than the transverse cross-sectional area of said rod at said first position, the density of said rod at said second position being greater than the density of said rod at said first position, e. said rod having an intermediate outer surface between said first and second positions, at least a portion of said intermediate outer surface being spaced from and lying within, said inner surface of said outer member, cavity means defined in part by said intermediate outer surface portion and a portion of said inner surface of said outer member and being closed at least at one end by portions of said circumferential ring, and f. the area of said intermediate outer surface portion being greater than the transverse cross-sectional area of said rod at said first position.
 2. A filter according to claim 1 characterized in that said area of said intermediate outer surface portion of said inner member is at least four times as great as said cross-sectional area of said rod at said first position.
 3. A filter according to claim 1 characterized in that said portion of substantially smaller cross sectional area is longitudinally spaced from the ends of the filter.
 4. A filter according to claim 1 characterized in that said portion of substantially smaller cross-sectional area lies at one end of the filter.
 5. A filter according to claim 4 characterized in that both ends of said inner member have a cross-sectional area substantially smaller than the intermediate portion.
 6. A filter according to claim 1 characterized in that at said second position the fibers are formed into ribs.
 7. A filter according to claim 6 characterized in that the ribs are arranged in the form of a cross.
 8. A filter according to claim 6 characterized in that the ribs are arranged in the form of a Y.
 9. A filter according to claim 6 characterized in that the tips of the ribs lie upon a circle, the diameter of which is approximately equal to the internal diameter of the said outer member.
 10. A filter according to claim 1 characterized in that between said first and second positions said intermediate outer surface portIon of said inner member through which the smoke passes is formed with protrusions or depressions.
 11. A filter according to claim 10 characterized in that the said protrusions or depressions comprise longitudinally directed ribs or valleys.
 12. A filter according to claim 1 characterized in that the fibers have a denier of less than
 5. 13. A filter according to claim 12 characterized in that the denier of the fibers is not greater than 2.5.
 14. A filter cigarette comprising a tobacco rod and a filter according to claim 1, said outer member of the filter comprising a tipping material which is wrapped around said inner member and extends over a part of the tobacco rod to attach the filter thereto.
 15. A filter according to claim 13 characterized in that the fibers are of cellulose acetate.
 16. A filter according to claim 1 in which the weight per unit length is substantially constant. 